FIG. 16 shows a general arrangement of a general continuous hot rolling line. Conventionally, changeover of coilers has been effected as described below when a strip cut to a predetermined length by a strip shear is coiled by the preceding material coiler and the following material coiler alternately. As an example, a case where coilers are changed over from the preceding material coiler a to the following material coiler b will be explained. A strip d sent from a finishing mill c is cut to a predetermined length by a strip shear e disposed on the downstream side of the finishing mill c to divide the strip d into the preceding strip d.sub.1 and the following strip d.sub.2. Then, the preceding strip d.sub.1 and the following strip d.sub.2 are coiled by the preceding material coiler a and the following material coiler b, respectively.
While the preceding strip d.sub.1 is coiled by the preceding material coiler a, a lower pinch roll g of a coiling pinch roll f disposed on the delivery side of the strip shear e is moved to the upstream side. Thereby, the offset angle of the coiling pinch roll f is changed to change the transfer direction of the strip from the preceding material coiler a to the following material coiler b. Immediately after the preceding strip d.sub.1 has gone through the coiling pinch roll f, the following strip d.sub.2 is introduced to the following material coiler b to coil the following strip d.sub.2 by using the following material coiler b. At this time, a triangular gate j prevents the following strip d.sub.2 from going to the side of the preceding material coiler a.
In recent years, as coiling equipment for continuous hot rolling, a Carrousel reel type coiler has been used.
FIG. 20 schematically shows an example of a continuous hot rolling line in which a Carrousel reel type coiler is used.
The Carrousel reel type coiler has a first and second mandrels 1 and 2. The first and second mandrels 1 and 2 are revolvably disposed at an interval in the circumferential direction on a revolution path 3 so that when one mandrel is located at a coiling start position, the other mandrel is located at a coiling finish position. For example, when the first mandrel 1 is located at the coiling start position, the preceding strip S.sub.1 sent from a finishing mill 4 is coiled by a predetermined amount by the first mandrel 1, and then the first mandrel 1 is revolved to the coiling finish position while coiling the preceding strip S.sub.1. In this state, the tail end of the preceding strip S.sub.1 is cut by a strip shear 5, and the leading end of the following strip S.sub.2 is coiled by the second mandrel 2 located at the coiling start position. After the coiling of the strip S.sub.1 is finished at the coiling finish position, the coil of the coiled preceding strip S.sub.1 is delivered from the mandrel 1, and the mandrel 1 waits until the leading end of a strip following the following strip S.sub.2 is coiled around the mandrel 1.
Above and below an upstream pass line P.sub.1 directed toward the mandrel at the coiling start position (the first mandrel 1 in the figure), upstream sheet-running guides 6 to 13 for guiding the leading end of the strip S toward the upstream mandrel are disposed. Above and below a downstream pass line P.sub.2 that branches off the upstream pass line P.sub.1 and is directed toward the mandrel at the coiling finish position (the second mandrel 2 in the figure), downstream sheet-running guides 13 to 15 and a guide roller 20 for guiding the strip S coiled by the mandrel at the coiling finish position are disposed. The sheet-running guide 13 is disposed at a position where the downstream pass line P.sub.2 branches off the upstream pass line P.sub.1 so as to be used as both an upper guide for the upstream pass line P.sub.1 and a lower guide for the downstream pass line P.sub.2.
In FIG. 20, reference numeral 16 denotes pinch rolls disposed on the pass line P.sub.1 between the finishing mill 4 and the strip shear 5, 17 denotes coiling pinch rolls disposed on the pass line P.sub.1 on the delivery side of the strip shear 5, 18 denotes upstream wrapper rolls disposed movably so as to come close to and go apart from the outer peripheral surface of the mandrel at the coiling start position, and 19 denotes downstream wrapper rolls disposed movably so as to come close to and go apart from the outer peripheral surface of the mandrel at the coiling finish position. The upstream and downstream wrapper rolls 18 and 19 and the upper guide 14 of the downstream sheet-running guide is movable so as to be separated from the revolution path 3 to allow the revolution of the first and second mandrels 1 and 2 when the mandrels 1 and 2 revolves on the revolution path 3.
In the conventional strip coiling method on the above-described general hot rolling line, however, when the strip is cut by the strip shear e, a tension given to the strip by the f inishing mill c and the preceding material coiler a is released, so that the tail end of the preceding strip is undesirably oversupplied on the delivery side of the coiling pinch roll f as shown in FIG. 17. In the worst case, there arises a problem in that the tail end of the preceding strip is caught by the triangular gate j, resulting in damage to the sheet. Further, there arises a problem in that after the tail end of the preceding strip S.sub.1 goes through the coiling pinch roll f, the circumferential speed of the coiling pinch roll f temporarily becomes lower than the transf er speed of the following strip S.sub.2, so that the leading end of the following strip S.sub.2 is oversupplied on the entrance side of the coiling pinch roll f.
On the other hand, even in the conventional strip coiling method on the hot rolling line on which the Carrousel reel type coiler is provided, if the preceding strip S.sub.1 is cut by the strip shear 5 while being coiled by the mandrel at the coiling finish position (the second mandrel 2), a tension given to the strip by the finishing mill 4 and the downstream mandrel is released, so that the preceding strip S.sub.1 is undesirably oversupplied on the delivery side of the coiling pinch rolls 17 disposed on the delivery side of the strip shear as shown in FIG. 21. In the worst case, there arises a problem in that the preceding strip S.sub.1 is caught by the tip end of the downstream sheet-running guide 13 located at a position where the downstream pass line P.sub.2 branches off the upstream pass line P.sub.1, resulting in damage to the sheet. Further, there arises a problem in that after the tail end of the preceding strip S.sub.1 goes through the coiling pinch rolls 17, the circumferential speed of the coiling pinch rolls 17 temporarily becomes lower than the transfer speed of the following strip S.sub.2, so that the leading end of the following strip S.sub.2 is oversupplied on the entrance side of the coiling pinch rolls 17.
The present invention has been achieved to solve the above problems, and accordingly an object thereof is to provide a strip coiling method in which after the tail end of a strip coiled by a mandrel is cut by a strip shear, the strip can be prevented from being oversupplied on the delivery side of coiling pinch rolls disposed on the delivery side of the strip shear, and the leading end of the following strip can be prevented from being oversupplied on the entrance side of the coiling pinch rolls.